Part 4: Clamps, Compliance & Current Range

3.5. Part 4: Clamps, Compliance & Current Range#

This is the forth introductory overview of programming the Aspect Device Engine Python API.
This document is available as pdf and interactive jupyter notebook. The introduction includes the following objectives:

  • Understanding the current range and clamps/compliance of idSMU devices

from aspectdeviceengine.enginecore import IdSmuService, IdSmuServiceRunner, IdSmuBoardModel, MeasurementMode, SmuCurrentRange, DpsCurrentRange, CurrentRange
import plotly.graph_objects as go
from plotly.subplots import make_subplots
import numpy as np
srunner = IdSmuServiceRunner()

mbX1 : IdSmuBoardModel = srunner.get_idsmu_service().get_first_board()
print(mbX1.is_board_initialized())
smu_channel = mbX1.idSmu2Modules['M1.S1'].smu.channels["M1.S1.C1"]
smu_channel.name = "ch1"
smu_channel.enabled = True

True

Python can always be used to analyse the properties and methods of an object.
We search for current range and clamp in the list, the topics of this tutorial:

# Let's list all properties and methods of the smu channel object
[m for m in dir(smu_channel) if not m.startswith('_')]

['autorange',
 'clamp_enabled',
 'clamp_high_value',
 'clamp_low_value',
 'current',
 'current_range',
 'enabled',
 'hardware_id',
 'measure_current',
 'measure_currents',
 'measure_voltage',
 'measure_voltages',
 'name',
 'output_ranges',
 'set_clamp_high_value',
 'set_clamp_low_value',
 'set_current',
 'set_name',
 'set_voltage',
 'voltage']

3.5.1. Current Range#

As an API user, you have the option of manually setting different current ranges.
It often makes sense to select a current range that is as close as possible to the current flowing through the DUT.
For small currents, the smallest possible matching current range should be selected.
This increases the accuracy when measuring a current. The two possible device types of an idSMU (SMU and DPS) each have different current ranges.

3.5.1.1. Setting and querying the current ranges#

The enum class for the current ranges only contains the respective valid members at channel level for SMU or DPS.
The enum at board level is a union of both.
In the latter case, the user is responsible for not selecting the wrong value.

print(list(SmuCurrentRange.__members__))
print(list(DpsCurrentRange.__members__))
print(list(CurrentRange.__members__))

['Range_5uA', 'Range_20uA', 'Range_200uA', 'Range_2mA', 'Range_70mA']
['Range_25uA', 'Range_250uA', 'Range_2500uA', 'Range_25mA', 'Range_500mA', 'Range_1200mA']
['Range_5uA', 'Range_20uA_SMU', 'Range_200uA_SMU', 'Range_2mA_SMU', 'Range_70mA_SMU', 'Range_25uA_DPS', 'Range_250uA_DPS', 'Range_2500uA_DPS', 'Range_25mA_DPS', 'Range_500mA_DPS', 'Range_1200mA_DPS']

The default value (after initialization) of a SMU based device is 70mA (and 500mA for a DPS device). The current_range property of a channel or the get_current_range() method of a board can be used to query the current range:

print(smu_channel.current_range)
print(mbX1.get_current_range("ch1"))

SmuCurrentRange.Range_70mA
CurrentRange.Range_70mA_SMU

The corresponding setter and board method are current_range and set_current_ranges()

smu_channel.current_range = SmuCurrentRange.Range_2mA
print(mbX1.get_current_range("ch1"))
mbX1.set_current_ranges(CurrentRange.Range_200uA_SMU, ["ch1"])
print(smu_channel.current_range)

CurrentRange.Range_2mA_SMU
SmuCurrentRange.Range_200uA

More about current ranges and autoranging in the next tutorial.

3.5.2. Current and voltage clamps#

An SMU or DPS channel has clamps. If a voltage is forced, the clamp is a current clamp.
If a current is forced (SMU types only), a voltage is clamped.
The clamp is active by default. We can check this with the ‘clamp_enabled’ property:

print(f'Is clamp enabled? {smu_channel.clamp_enabled}')

Is clamp enabled? True

In voltage force mode, the default clamp value is 70mA

print(f'The default upper clamp value is {smu_channel.clamp_high_value}A')

The default upper clamp value is 0.07A

To see the clamp in action, the voltage is swept across an LED and the current is measured (more on IV sweeps in the next chapters).
The clamp is first set to 100uA and the current range is adjusted to this current range:

currents = np.zeros(40);voltages = np.zeros(40)
smu_channel.clamp_enabled = True

smu_channel.clamp_high_value=0.0001
# an alternative to set lower and upper clamp together is to use the board method:
# mbX1.set_clamps_low_and_high_values(-0.001, 0.0001, ["ch1"])
smu_channel.current_range = SmuCurrentRange.Range_200uA
for i in range(1,40):
    smu_channel.voltage = 2.0+0.2*i
    currents[i] = smu_channel.current
    voltages[i] = smu_channel.voltage

As can be seen in the plot, the clamp becomes active slightly above the set maximum.

fig = make_subplots(rows=1, cols=2,  subplot_titles=("LED current", "LED voltage"))
fig.add_trace(go.Scatter(x=np.arange(1,40), y=currents,
                    mode='lines+markers+text',
                    textposition="top center",
                    name='LED current'),  row=1, col=1)
fig.add_trace(go.Scatter(x=np.arange(1,40), y=voltages,
                    mode='lines+markers+text',
                    textposition="top center",
                    name='LED voltage'),  row=1, col=2)
fig.update_layout(height=600)
fig.update_xaxes(title_text="Step", row=1, col=1);fig.update_yaxes(title_text="Current [A]", row=1, col=1)
fig.update_xaxes(title_text="Step", row=1, col=1);fig.update_yaxes(title_text="Coltage [V]", row=1, col=2)
fig
#uncomment in pure python script:
#fig.show()

The clamp will now be disabled and the current measurement will be repeated:

currents = np.zeros(40);voltages = np.zeros(40)

smu_channel.clamp_high_value=0.0001
smu_channel.clamp_enabled = False
smu_channel.current_range = SmuCurrentRange.Range_2mA
for i in range(1,40):
    smu_channel.voltage = 2.0+0.2*i
    currents[i] = smu_channel.current
    voltages[i] = smu_channel.voltage

fig = make_subplots(rows=1, cols=2,  subplot_titles=("LED current", "LED voltage"))
fig.add_trace(go.Scatter(x=np.arange(1,40), y=currents,
                    mode='lines+markers+text',
                    textposition="top center",
                    name='LED current'),  row=1, col=1)
fig.add_trace(go.Scatter(x=np.arange(1,40), y=voltages,
                    mode='lines+markers+text',
                    textposition="top center",
                    name='LED voltage'),  row=1, col=2)
fig.update_layout(height=600)
fig.update_xaxes(title_text="Step", row=1, col=1);fig.update_yaxes(title_text="Current [A]", row=1, col=1)
fig.update_xaxes(title_text="Step", row=1, col=1);fig.update_yaxes(title_text="Coltage [V]", row=1, col=2)
fig
#uncomment in pure python script:
#fig.show()

srunner.shutdown()
Contents